1. Field of the Invention
This invention relates to pressure-actuated valves which are remotely controlled such as by use of a solenoid to open or close a pilot valve, and more particularly relates to means to control the rate that these valves close.
2. Brief Description of the Prior Art
Pressure-actuated valves with which the present invention has unique application are well known in the art. They are normally comprised of a diaphragm suspended plug member with the diaphragm and plug member forming a control chamber. When the chamber is filled with fluid the plug member is forced against its seat and the valve is closed. When the chamber is substantially empty, the plug member is positioned away from its seat and the valve is open.
The conventional means of opening and closing the valve are a restricted inlet port to the valve control chamber and a pilot valve which vents the control chamber into the low pressure side of the line. When the pilot valve is initially opened, fluid will flow from the valve chamber faster than it enters through inlet port thereby opening the valve until the flow into the central chamber equalizes with the flow out of the control chamber. When the pilot valve is closed, fluid flows into the control chamber without flowing out thereby gradually forcing the valve plug against the valve seat.
Some of these pressure actuated valves include means to control the rate the valve closes, mainly by means of restricting the rate of fluid flow into the control chamber as the valve closes. If the flow into this chamber is unrestricted, the chamber will fill rapidly and the valve will close rapidly. This rapid closing must be avoided in most applications because it causes a pressure shock in the fluid in the line. This pressure shock can cause the pipes to burst when they are in a weakened condition. It also causes excess wear and tear on the closing valve as well as on other valves in the line.
If the passageway into the valve control chamber is highly restricted, the valve will close very slowly at a substantially uniform rate. This uniform rate is normally not necessary because the shock effect occurs when the valve is nearly closed. Therefore a variable rate of fluid flow restrictor is usually provided to allow the valve to close rapidly when it is open and slower when it is nearly closed.
Attempts of providing a variable restriction to the flow of fluid through the inlet port have included plungers which enter the inlet port as the valve closes. The plunger substantially and abruptly reduces the cross sectional area of the inlet port thereby reducing the rate of flow into the valve control chamber. However, an abrupt change in the closing rate of the valve is undesirable because the abrupt change itself causes undesirable transients in the line.
Other attempts of providing a variable restriction to the flow of fluid through the inlet port have provided the plunger within the inlet port at the time the plug begins its motion to the closed position. Variable restriction in flow is provided by having the inlet port be a narrow passageway which is increasingly filled by the plunger as the valve closes. These narrow passageways are susceptible to being clogged by foreign matter in the fluid, especially in applications involving irrigation systems where the water is "filthy" with dirt and other materials. These plunger/narrow passageway restrictors therefore tend to become inoperable over time. Consequently the valves using plungers in narrow passageways require the use of preliminary dirt filters in order to provide a useful life for the valve.